Prior art videoconference systems fall into two categories.
A first category comprises professional point-to-point and point-to-multipoint systems, which use a digital telephone-network such as the ISDN and conform to the H320 standard. They enable users to contact one another using their telephone subscriber numbers. They are limited by the capacity of an ISDN line, which is at most twice 64 kbit/s. It is possible to couple a plurality of ISDN lines together to increase capacity, but this leads to an increase in the cost of using the system.
A second category comprises consumer systems using the Internet and conforming to the H323 standard, for example. These systems exploit the high capacity of the offers from Internet service providers (ISP). Using asymmetric digital subscriber line (ADSL) technology, these offers provide capacities of 64 kbit/s in the uplink direction and 128 kbit/s in the downlink direction, or even 256 kbit/s and 1024 kbit/s, respectively. The methods employed by these systems provide very good picture and sound quality, but they do have drawbacks. One of the more important drawbacks is that their bit rate is not guaranteed. However, since these offers are based on a fixed charge for access to the Internet, calls cost the user nothing. Moreover, when executed by a computer, these methods require the user to have some knowledge of the underlying technicalities of computer identification on the Internet, and more generally on any IP network. Obtaining a fixed IP address that identifies a computer permanently is a costly operation for a consumer. This leads to the use of temporary IP addresses assigned to the user by the service provider. This address is not only temporary but also assigned for a period that is unknown to the user, which is reflected in unilateral withdrawal of the address at the initiative of the ISP at the end of that period. Although the user may immediately demand another IP address, and obtain it quickly, this withdrawal of the IP address without warning suddenly breaks off any videoconference that might be in progress.
Users wishing to interconnect in an IP videoconference may simplify their task by using dynamic domain name servers (DNS) which indicate the latest IP address assigned to a computer, provided that the symbolic name given to the computer is known. This method therefore enables the IP address of the computer with which the videoconference must be established to be recovered by interrogating a dynamic DNS. However, it has the following drawbacks. Firstly, the user must know the addresses of the dynamic DNSes. Secondly, each computer must declare itself to the dynamic DNS(es) so that they can identify it (them). Moreover, the user must know the symbolic name of the computer that is to be connected in a videoconference. Furthermore, the dynamic DNSes must be available for users to be able to interrogate them. Finally, this method necessitates intermediate equipment for setting up a videoconference between two computers.